Async Observable method inside of a map method

Question

What's the best approach to transform an array and call few observable methods inside.

What I am looking for is something of this type to work:

   resultArray = someArray.map(item => {
      oneObs.subscribe(result1 => {
           item.result1 = result1
      });
      secondObs.subscribe(result2 => {
           item.result2 = result2
      });
   });

What is the best approach here? I came up only with a workaround to use the forEach loop of this kind:

   someArray.forEach(item => {
      Observable.forkJoin([oneObs, secondObs]).subscribe(
        (results: [Result1Type, Result2Type]) => {
           item.result1 = results[0];
           item.result2 = results[1];
           resultArray.push(item);
       });
    });

Any help appreciated.

Jon G Stødle · Accepted Answer · 2017-08-16 08:52:55Z

4

Your trying to mix synchronous and asynchronous code, which might lead to some weird behavior. My recommendation would be to convert the array to an observable (making the array asynchronous) getting the results and then converting the completed result to an array again:

Observable.from(someArray) // 1
    .mergeMap(item => Observable.forkJoin(oneObs, twoObs)
            .map(results => {
                item.result1 = results[0];
                item.result2 = results[1];
                return item;
            }))
    .toArray() // 2
    .subscribe(arr => resultArray = arr);

Create an observable based on the array
Wait for all observables to finish and create an array with all the resulting values

answered Aug 16, 2017 at 8:52

Jon G Stødle

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